1. Field of the Invention
The invention refers to an apparatus for testing integrated circuits according to the preamble of patent claim 1.
2. Description of Prior Art
The conducting paths or contact points of integrated circuits (IC) are arranged with a predetermined pitch. In case of highly integrated ICs a progressively smaller pitch is applied. In the manufacturing of ICs it is necessary to test the accuracy and function after fabrication. For this, test apparatuses have been developed by which a temporary connection with all leads or contacts can be established in order to test the geometrical position of contact points and the function of the integrated elements, respectively.
It is also known in connection with such test apparatuses to arrange two parallel plates at a distance from each other which have a pattern of aligned bores. End portions of resilient contact elements are sitting in the bores. An IC to be tested is received on the outer side of a plate in a predetermined positional relation in order to bring the pattern of end portions of the contact elements in engagement with the pattern of contact points of the IC. By means of a pressure member the IC chip is pressed against the contact elements which form springs. In the known testing apparatus the contact elements are cut out of sheet material and have coaxial end portions and a center portion which is arcuately curved in the plane of the sheet material strip. The end portion of the contact elements facing the pressure member extends slightly beyond the outer side of the plate. If upon engagement of the contact points of the IC with the contact elements of the test apparatus an axial pressure is exerted on the contact elements, the center portion of the contact elements between the plates is deformed, contemporaneously a pressure electrical contact is generated between the contact elements and the contact points of the chip. The The areal moment of inertia of the known contact elements in bending direction is relatively high so that they have to have a deep arc or slope in the center portion to secure that the spring force does not exceed a predetermined value. It is not possible to reduce the spring force in that the material has a smaller thickness. To achieve a controlled bending, the sheet material from which the contact elements are cut out has to have a thickness of at least 0.25 to 0.4 mm. The explained shape of the contact elements means that, upon arrangement in a line one after the other, the distance of the contact points from each other cannot be below a minimum value. This minimum distance is so large that in case of IC chips having a small pitch the known contact elements cannot be used. A narrower distance between the contact points of the IC chips can be tested with the known apparatus only if the contact points are located offset, e.g. in a staggered formation rather than in form of a chess board pattern. It is understood that such an arrangement does not allow a high packing density as a chess board distribution.
The object of the invention is to provide an apparatus for testing of IC chips which allows a satisfactory testing also with very low pitched chips.
This object is attained by the features of the characterizing portion of patent claim 1.